Tunnel field effect transistor (tfet) with lateral oxidation

ABSTRACT

A vertical-mode tunnel field-effect transistor (TFET) is provided with an oxide region that may be laterally positioned relative to a source region. The oxide region operates to reduce a tunneling effect in a tunnel region underlying a drain region, during an OFF-state of the TFET. The reduction in tunneling effect results in a reduction or elimination of a flow of OFF-state leakage current between the source region and the drain region. The TFET may have components made from group III-V compound materials.

STATEMENT REGARDING GOVERNMENT SPONSORED RESEARCH OR

DEVELOPMENT

The work described herein was sponsored at least in part by the EmergingTechnology Fund of Texas, Project “UT Dallas Sub: High-K III-V MOSFETs,”grant no. UTD 09-10. The state of Texas may have certain rights to thesubject matter disclosed herein.

BACKGROUND

As metal-oxide-semiconductor transistors (MOSFETs) are aggressivelyscaled to smaller size, the performance of such MOSFETs may besignificantly limited by short channel effects and gate leakage current.Short channel effects arise if channel lengths of MOSFETs are reduced byscaling in an attempt to increase both operational speed and a number ofMOSFETs per chip. Threshold voltages of MOSFETs become more difficult tocontrol, due at least in part to a modification of the threshold voltagecaused by the shortening of the channel lengths as a result of scaling.With regards to gate leakage current, scaling reduces a thickness of agate oxide of a MOSFET, but the decreased thickness of the gate oxidecauses an amount of the gate leakage current to increase during anOFF-state of the MOSFET. The increased amount of gate leakage currentdisadvantageously results in increased power consumption.

In addition to short channel effects and increased gate leakage current,there are other challenges with MOSFETs. As one example, MOSFETs have ahigh subthreshold swing, typically greater than 60 mV/decade. Thesubthreshold swing is generally defined as a level of gate voltage tochange a drain current by one order of magnitude (e.g., by one decade),and with scaling to reduce a MOSFET's size, the subthreshold swingincreases. A disadvantageous consequence of an increased subthresholdswing is that a higher power supply voltage may be needed to turn ON theMOSFET. Another disadvantage of an increased subthreshold swing is anincrease in leakage current during an OFF-state of the MOSFET. Supplyvoltage scaling is another example of a challenge with MOSFETs. It isoften difficult to scale (decrease or increase) a level of supplyvoltage (e.g., V_(DD)) provided to a MOSFET based on the particularapplication or use of the MOSFET. Thus, V_(DD) scaling limitations mayreduce the capability to provide an optimum supply voltage V_(DD) to areduced-size MOSFET for a low-power digital application.

In comparison to MOSFETs, tunneling field-effect transistors (TFETs)having a gate-modulated Zener tunnel region may provide subthresholdswings of less than 60 mV/decade and may operate at a lower supplyvoltage V_(DD). Thus, TFETs are considered as potential candidates toreplace MOSFETs in low-power digital applications.

However, most silicon (Si)-based or silicon-germanium (SiGe)-based TFETsexhibit low ON-state current. For example, there is a high tunnelingbarrier in the tunnel region of Si-based and SiGe-based TFETs, due atleast in part to the large bandgap of the material of the tunnel region.This high tunneling barrier is characterized by a smaller amount ofelectrons moving through the tunnel region, thereby resulting in reducedON-state current that in turn results in slower operating speed of theSi-based and SiGe-based TFETs.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter is particularly pointed out and distinctly claimed in theconcluding portion of the specification. The foregoing and otherfeatures of this disclosure will become more fully apparent from thefollowing description and appended claims, taken in conjunction with theaccompanying drawings. Understanding that these drawings depict onlyseveral embodiments in accordance with the disclosure and are,therefore, not to be considered limiting of its scope, the disclosurewill be described with additional specificity and detail through use ofthe accompanying drawings.

The sizes and relative positions of elements in the drawings are notnecessarily drawn to scale. For example, the shapes of various elementsand angles may not be drawn to scale, and some of these elements andangles may be arbitrarily enlarged and positioned to improve drawinglegibility. Further, the particular shapes of the components as drawn,are not intended to convey any information regarding the actual shape ofthe particular component, and have been solely selected for ease ofrecognition in the drawings.

Various embodiments will be described referencing the accompanyingdrawings in which like references denote similar elements, and in which:

FIG. 1 is a diagrammatic sectional view of a tunnel field-effecttransistor (TFET), in accordance with various embodiments;

FIG. 2 is a diagrammatic top view of the TFET of FIG. 1, in accordancewith various embodiments;

FIG. 3 is a flowchart of a method to manufacture the TFET of FIG. 1, inaccordance with various embodiments;

FIG. 4 is a diagrammatic sectional view of a structure formed using afirst step of the method of FIG. 3, in accordance with variousembodiments;

FIG. 5 is a diagrammatic sectional view of a structure formed using asecond step of the method of FIG. 3, in accordance with variousembodiments;

FIG. 6 is a diagrammatic sectional view of a structure formed using athird step of the method of FIG. 3, in accordance with variousembodiments;

FIG. 7 is a diagrammatic sectional view of a structure formed using afourth step of the method of FIG. 3, in accordance with variousembodiments;

FIG. 8 is a diagrammatic sectional view of a structure formed using afifth step of the method of FIG. 3, in accordance with variousembodiments;

FIG. 9 is a diagrammatic sectional view of a structure formed using asixth step of the method of FIG. 3, in accordance with variousembodiments;

FIG. 10 is flowchart of a method of operating the TFET 100 of FIG. 1, inaccordance with various embodiments; and

FIG. 11 is an example computing device suitable for practicing variousembodiments.

DETAILED DESCRIPTION

The following description sets forth various examples along withspecific details to provide a thorough understanding of claimed subjectmatter. It will be understood, however, the claimed subject matter maybe practiced without some or more of the specific details disclosedherein. Further, in some circumstances, well-known methods, procedures,systems, components and/or circuits have not been described in detail inorder to avoid unnecessarily obscuring claimed subject matter. In thefollowing detailed description, reference is made to the accompanyingdrawings, which form a part hereof. In the drawings, similar symbolstypically identify similar components, unless context dictatesotherwise. The illustrative embodiments described in the detaileddescription, drawings, and claims are not meant to be limiting. Otherembodiments may be utilized, and other changes may be made, withoutdeparting from the spirit or scope of the subject matter presented here.It will be readily understood that the aspects of the presentdisclosure, as generally described herein, and illustrated in theFigures, may be arranged, substituted, combined, and designed in a widevariety of different configurations, all of which are explicitlycontemplated and make part of this disclosure.

With respect to the use of substantially any plural and/or singularterms herein, it is possible to translate from the plural to thesingular and/or from the singular to the plural as is appropriate to thecontext and/or application. The various singular/plural permutations maybe expressly set forth herein for sake of clarity.

This disclosure is drawn, inter alia, to a structural arrangement of atunnel field-effect transistor (TFET) having lateral oxidation tocontrol tunneling effect in a tunnel region of the TFET, a method ofoperating such a TFET, and a method of manufacturing such a TFET.

As an overview, the TFET of some embodiments has lateral oxidation thatoperates to reduce OFF-state leakage current flow of the TFET.Furthermore, at least some components of the TFET of some embodimentsare made from group III-V compound materials, which have physicalproperties that enable an increased level of ON-state current throughthe tunnel region of the TFET. By having the lateral oxidation and thecomponents made from group III-V materials, the TFET of some embodimentalso addresses at least some of the disadvantages of MOSFETs andSi-based and SiGe-based TFETs described above. In various embodiments,the TFET may have a vertical arrangement of some of its components.

FIG. 1 is a diagrammatic sectional view of a TFET 100, in accordancewith various embodiments of the present disclosure. In some embodiments,components of the TFET 100 may comprise a drain region 102, a channelregion 104, a tunnel region 106, a source region 108, an oxide region110, and a substrate 112. Furthermore, the TFET 100 of some embodimentsmay further comprise a gate region 114, a gate oxide layer 116, and apassivation layer 118.

The TFET 100 of some embodiments may have a generally “vertical”arrangement (referred to herein as “vertical-mode”) of at least some ofits components. For example, the source region 108, the channel region104, and the drain region 102 may be vertically stacked over thesubstrate 112 in some embodiments.

In some embodiments of the TFET 100, the channel region 104 may becoupled to the drain region 102, and may for example vertically underliethe drain region 102 in some embodiments of a vertical-mode TFET, suchas shown by way of example in FIG. 1. The tunnel region 106 of someembodiments may have a portion, with a width generally corresponding toa width X of the oxide region, coupled to the channel region 104 and tothe drain region 102. The portion (of the tunnel region 106) having awidth generally corresponding to the width X may, for example,vertically underlie the drain region 102 and the channel region 104 insome embodiments of a vertical-mode TFET, such as shown by way ofexample in FIG. 1. The tunnel region 106 may be further coupled to thesource region 108.

In some embodiments, the oxide region 110 may be positioned at leastpartially under the drain region 102, the channel region 104, and theportion of the tunnel region 106 underlying the drain region 102, andmay further be positioned laterally relative to the source region 108.The purpose(s) for positioning the oxide region 110 at these locationswill be explained in detail below.

In some embodiments of the TFET 100, for example in a vertical-modeTFET, the gate region 114 may vertically overlie at least some of thesource region 108 and at least some of the tunnel region 106.Furthermore, in some embodiments such as shown by way of example in FIG.1, the gate region 114 may be laterally displaced relative to the drainregion 102, so that the gate region 114 may not vertically overlie allor most portions of the drain region 102. The gate oxide layer 116 ofsome embodiments may be positioned between the gate region 114 and anyone or more of the source region 108, the tunnel region 106, thepassivation layer 118, the channel region 104, and the drain region 102.

The passivation layer 118 of some embodiments may be positioned betweenthe channel region 104 and the tunnel region 106, and may operate toprovide an improved physical interface or improved coupling with thegate oxide layer 116. The passivation layer 118 may be made of indiumphosphide (InP), for example, or other suitable materials that would befamiliar to those skilled in the art having the benefit of thisdisclosure.

The TFET 100 of some embodiments may further comprise a source contact120 coupled to the source region 108, and a drain contact 122 coupled tothe drain region 102. A supply voltage V_(DD) (not shown) may be appliedto the drain region 102 by way of the drain contact 122. In someembodiments, a supply voltage V_(G) (not shown) may be applied to thegate region 114. In some embodiments, a supply voltage V_(SS) (notshown) may be applied to the source region 108 by way of the sourcecontact 120.

According to some embodiments, the source contact 120 and the draincontact 122 may be made from a suitably conductive metal, such as a goldgermanium/nickel/gold (AuGe/Ni/Au) contact. The gate region 114 may bemade from a metal, such as tantalum nitride (TaN) as an example or fromsome other suitable material that would be familiar to those skilled inthe art having the benefit of this disclosure. For instance, additionalpossible materials that may be used for the source contact 120, thedrain contact 122, and/or the gate region 114 may include, but not belimited to, tungsten, copper, gold, silver, tin, highly doped silicon,aluminum (Al), or other materials or combination thereof. The gateoxide, if present in some embodiments, may be made, for example, fromsilicon dioxide (SiO₂), aluminum oxide (Al₂O₃), or other suitable oxidematerial that would be familiar to those skilled in the art having thebenefit of this disclosure.

According to some embodiments, at least some of the components of theTFET 100 may be made from a group III-V compound material. For example,at least one of the drain region 102, the channel region 104, thepassivation layer 118, the tunnel region 106, the source region 108, orthe substrate 112 may be made from a group III-V compound material insome embodiments. In some embodiments, the oxide region 110 may be madefrom a group III-V compound material that has been oxidized, as will bedescribed in detail below. In some embodiments, the substrate 112 may bemade from some other material, such as silicon (Si), instead of a groupIII-V compound material.

Examples of group III-V compound materials that can be used for thedrain region 102, the channel region 104, the passivation layer 118, thetunnel region 106, the source region 108, the substrate 112, or theoxide region 110 (prior to oxidation) include but are not limited to:aluminium antimonide (AlSb), aluminium arsenide (AlAs), aluminiumnitride (AlN), aluminium phosphide (AlP), boron nitride (BN), boronphosphide (BP), boron arsenide (BAs), gallium antimonide (GaSb), galliumarsenide (GaAs), gallium nitride (GaN), gallium phosphide (GaP), indiumantimonide (InSb), indium arsenide (InAs), indium nitride (InN), indiumphosphide (InP), aluminium gallium arsenide (AlGaAs), indium galliumarsenide (InGaAs), indium gallium phosphide (InGaP), aluminium indiumarsenide (AlinAs), aluminium indium antimonide (AlInSb), galliumarsenide nitride (GaAsN), gallium arsenide phosphide (GaAsP), aluminiumgallium nitride (AlGaN), aluminium gallium phosphide (AlGaP), indiumgallium nitride (InGaN), indium arsenide antimonide (InAsSb), indiumgallium antimonide (InGaSb), aluminium gallium indium phosphide(AlGaInP), aluminium gallium arsenide phosphide (AlGaAsP), indiumgallium arsenide phosphide (InGaAsP), aluminium indium arsenidephosphide (AlInAsP), aluminium gallium arsenide nitride (AlGaAsN),indium gallium arsenide nitride (InGaAsN), indium aluminium arsenidenitride (InAlAsN), gallium arsenide antimonide nitride (GaAsSbN),gallium indium nitride arsenide antimonide (GaInNAsSb), or galliumindium arsenide antimonide phosphide (GaInAsSbP).

In some embodiments, a combination of group III-V compound materialsthat may be used for the TFET 100 are indium gallium arsenide (InGaAs)for the tunnel region 106 and aluminum gallium arsenide (AlGaAs) oraluminium indium arsenide (AlinAs) for the drain region 102, the sourceregion 108, or the channel region 104. In some embodiments, the oxideregion 110 may be made from the same or substantially similar groupIII-V material as the source region 108, such as AlGaAs that has beenoxidized to form aluminum oxide (AlO₂).

The group III-V compound materials and/or other materials that make upthe components of some embodiments of the TFET 100 may in turn be dopedwith a dopant (such as by using an ion implantation technique) so as tohave certain doping concentrations, thereby providing the appropriateelectrical/transistor functionality for the TFET 100. For instance insome embodiments, the drain region 102 may be made from a heavily dopedgroup III-V compound material of a first conductivity type (for example,to provide an n-type drain region 102); the channel region 104 may bemade from a lightly doped group III-V compound material of the firstconductivity type; the passivation layer 118 may be made from a compoundmaterial of the first conductivity type; the tunnel region 106 may bemade from another heavily doped group III-V compound material of thefirst conductivity type; and the source region 108 may be made from aheavily doped group III-V compound material of a second conductivitytype different from the first conductivity type (for example, to providea p-type source region 108). In some embodiments of the TFET 100 thatprovide a group III-V compound material for the substrate 112, thesubstrate 112 may be made from a semi-insulating (SI) material or aheavily doped group III-V compound material of the second conductivitytype.

The concentration and type of dopant used in order to provide a “heavilydoped” (n+ or p+) material or a “lightly doped” (n− or p−) materialwould be familiar to those skilled in the art having the benefit of thisdisclosure. In some embodiments according to the above-described doping,the drain region 102 may be n+ AlGaAs; the channel region 104 may be n−AlGaAs; the tunnel region 106 may be n+ InGaAs; and the source region108 may be p+ AlGaAs.

In comparison to Si-based or SiGe-based TFETs previously discussed,embodiments of the TFET 100 using group III-V compound materials mayenable higher ON-state current. For example, the group III-V compoundmaterial of the tunnel region 106 provides lower tunneling barrier dueto a smaller bandgap, as compared to the tunnel region of Si-based orSiGe-based TFETs that have larger bandgaps and therefore have moreprominent resistive or insulating effects through their tunnel regions.The smaller bandgap and a smaller effective electron mass of group III-Vcompound materials result in increased conductivity (characterized byfaster movement of electrons) through the tunnel region 106 and hencethe ON-state current for some embodiments of the TFET 100 may beincreased. The increased ON-state current thus enables some embodimentsof the TFET 100 to have faster operating speeds.

The TFET 100 of some embodiments addresses a drawback of someconventional transistors that have significant leakage current during anOFF-state of such transistors. For example with conventional TFETs, thedirection of flow of the OFF-state leakage current is between a sourceregion and a drain region and is outside the gate control, and through atunnel region and a channel region. A tunneling effect of the tunnelregion undesirably enables substantive OFF-state leakage current to moreeasily flow between the source region and the drain region through thechannel region during an OFF-state of the conventional TFETs. To reducethis substantive OFF-state leakage current, conventional TFETs are madewith a longer/thicker channel region. The longer/thicker channel regionnegates the effect of the drain voltage alone that would otherwisefacilitate OFF-state leakage current flow, since the drain voltage hasto drop across the longer/thicker channel region, and reduces thetunneling current in the region outside the gate control. However, suchlonger/thicker channel regions also result in a reduction of ON-statecurrent, due to longer effective channel length and higher channelresistance. Thus, the length/thickness of channel regions may not beaggressively scaled down in conventional TFETs or else OFF-state leakagecurrent may become more prominent.

Accordingly, the TFET 100 of various embodiments provides the oxideregion 110 such as shown by way of example in FIG. 1. The oxide region110 of some embodiments, such as in a vertical-mode TFET configurationdescribed above and shown in FIG. 1, is positioned so as to operate asan insulator to block or otherwise reduce OFF-state leakage current thatmay flow in a direction between the source region 108 and the drainregion 102 through the channel region 104 and the tunnel region 106 andoutside the gate control. In some embodiments, for example, the oxideregion 110 is positioned at least partially under the drain region 102.This position of the oxide region 110 reduces or eliminates thecapability of the OFF-state leakage current to use the tunneling (whichwould otherwise be provided under the drain region 102 by the portion ofthe tunnel region 106 spanning the width X) for a current path.

In some embodiments, such as in a vertical-mode TFET 100 shown in FIG.1, electrical fields from the drain region 102 emanate in a generallydownward direction across the channel region 104. Any potentialOFF-state leakage current may flow along a current path that followssuch electrical fields. Accordingly, the width X of the oxide region 110may be suitably designed to block or otherwise restrict the current path(of the potential OFF-state leakage current) that follows the generallydownward direction of the electrical fields from the drain region 102.

Furthermore in some embodiments, the presence of the oxide region 110may enable a length/thickness Y of the channel region 104 to be reduced.For instance, the insulating effect of the oxide region 110 reduces oreliminates a need for a longer length/thickness of the channel region104 that would otherwise have been used to reduce OFF-state leakagecurrent flow. Hence, the length/thickness Y of the channel region 104 ofsome embodiments of the TFET 100 may be scaled down. As an example forsome embodiments, the length/thickness Y of the channel region 104 maybe reduced from approximately 5 nm-100 nm, to approximately 1 nm-50 nm.This reduced thickness/length Y of the channel region 104 enablesON-state current of the TFET 100 to be increased, thereby resulting infaster operational speed. The capability to provide (a) increased orhigher ON-state current, (b) a subthreshold swing of less than 60mV/decade, (c) a reduced OFF-state leakage current, and/or (d) a smallersize thus enables a TFET 100 (having components made from group III-Vcompound materials) of some embodiments to be well-suited for low-power,low-operating-voltage digital applications.

In some embodiments, the width X of the oxide region 110 may beapproximately equal to a width Z of the drain region 102 so as tounderlie substantially an entirety of the drain region 102, and may begreater or lesser than the width Z by some nominal amount. In someembodiments, the width X of the oxide region 110 may differ from (e.g.,may be greater than or less than) the width Z of the drain region 102 byapproximately 3% to 30%. The amount of a difference, if any, between thewidth X and the width Z may be influenced by a variety of factorsrelated to an operationally acceptable performance level of someembodiments of the TFET 100. For example, in some implementations, ahigher level of OFF-state leakage current may be operationallyacceptable and/or a longer length/thickness Y of the channel region 104may be operationally acceptable, and so the width X of the oxide region110 may be designed to be substantially less than the width Z of thedrain region 102. As another example, a particular low level ofOFF-state leakage current and/or a particular level of ON-state currentmay be desired for a certain application, and so the width X of theoxide region 110 alone or in combination with the length/thickness Y ofthe channel region 104 may be chosen so as to achieve the particular lowlevel of OFF-state leakage current and/or the particular level ofON-state current.

FIG. 2 is a diagrammatic top view of the TFET 100 of FIG. 1, inaccordance with various embodiments. The gate region 114 is shown in theshaded area, and at least a portion of the tunnel region 106 mayunderlie the gate region 114 and the extent (shown in by a broken line)in which the tunnel region 106 may underlie the gate region may bedefined by an etching process, described later below. The channel region104 may underlie the drain region 102, such that the footprint of thedrain region 102 may be approximately the same as the footprint of thechannel region 104.

With respect to the oxide region 110, FIG. 2 illustrates an embodimentwherein the width X of the oxide region 110 may be approximately equalto the width Z of the drain region 102. Furthermore, FIG. 2 illustratesan embodiment wherein a dimension W (such as a depth) of the oxideregion 110 may be approximately equal to the depth of the drain region102. Thus, in the embodiment illustrated in FIG. 2, the oxide region 110may have substantially the same footprint as the drain region 102 and/orthe channel region 104.

FIG. 3 is a flowchart of a method 300 to manufacture the TFET 100 ofFIG. 1, in accordance with various embodiments. FIGS. 4-9 arediagrammatic sectional views of a structure that is obtained after eachstep of the method 300 to manufacture the TFET of FIG. 1, in accordancewith various embodiments. It is understood that various elements of thedepicted method 300 may not necessarily be performed in the exact orderthat is shown. Moreover, certain elements of the method 300 may beadded, removed, or modified in some embodiments.

FIG. 4 is a diagrammatic sectional view of a structure formed using afirst step 302 of the method 300 of FIG. 3, in accordance with variousembodiments. In the first step 302 in FIG. 3 and also as shown by theresulting structure in FIG. 4, a source layer 400, a tunnel layer 402,the passivation layer 118, a channel layer 404, and a drain layer 406may be formed over the substrate 112. In some embodiments, molecularbeam epitaxy (MBE) may be used to form these layers on the substrate112, including using MBE to epitaxially grow at least some of theselayers using group III-V compound materials.

FIG. 5 is a diagrammatic sectional view of a structure formed using asecond step 304 of the method 300 of FIG. 3, in accordance with variousembodiments. In the second step 304 in FIG. 3 and also as shown by theresulting structure in FIG. 5, different kinds of etching techniques maybe used to etch away a first portion 500 of the drain layer 406, thechannel layer 404, the passivation layer 118, the tunnel layer 402, andthe source layer 400 down to the substrate 112. In some embodiment, amesa etching technique, an anisotropic etching technique, or otherdirectional etching technique may be used. In some embodiments, a wetetching technique, an isotropic etching technique, or other techniquemay be used to remove the first portion 500.

FIG. 6 is a diagrammatic sectional view of a structure formed using athird step 306 of the method of FIG. 3, in accordance with variousembodiments. In the third step 306 in FIG. 3 and also as shown by theresulting structure in FIG. 6, the oxide region 110 may be formed bylaterally oxidizing the same starting material as the source layer 400.For example in some embodiments, lateral oxidation may be performed onat least some portion of the source layer 400 that is positioned next tothe first portion 500 that was etched away in FIG. 5.

In some embodiments, the lateral oxidation of FIG. 6 may be performedusing thermal oxidation (or other wet oxidation process), in which thematerial of the source layer 400 (such as a group III-V compoundmaterial) reacts with water vapor, carried by nitrogen gas, so as toform an oxide. In some embodiments, the time and/or temperature toperform the lateral oxidation may be based at least in part on factorssuch as the type of material being oxidized, a desired width X of theoxide region 110, or other considerations. As an example, for someembodiments that use AlGaAs as the group III-V material for the sourcelayer 400, the lateral oxidation may be performed at approximately 400degrees Celsius. Other temperatures are possible, such as approximately425 degrees Celsius, approximately 450 degrees Celsius, or othertemperatures. In some embodiments, lateral oxidation of the source layer400 may exhibit a generally linear oxidation rate at one or more ofthese temperatures. For instance, at approximately 400 degrees Celsiusfor AlGaAs material that is approximately 80 nm thick: approximately 100minutes of lateral oxidation may be used to obtain a widthX=approximately 15 microns, approximately 200 minutes of lateraloxidation may be used to obtain a width X=approximately 25 microns,approximately 300 minutes of lateral oxidation may be used to obtain awidth X=approximately 35 microns, and so forth.

In a fourth step 308 in FIG. 3, an etching process may be used to etch asecond portion of the drain layer 406, the channel layer 404, thepassivation layer 118, and the tunnel layer 402 down to the source layer400. FIG. 7 is a diagrammatic sectional view of a structure formed usingthe fourth step 308 of the method 300 of FIG. 3, in accordance withvarious embodiments. In FIG. 7, the etching process of the fourth step308 of FIG. 3 has removed the second portion (shown at 700) so as toform the source region 108 from the source layer 400 of FIG. 6 and thetunnel region 106 from the tunnel layer 402 of FIG. 6. In someembodiment, a mesa etching technique, an anisotropic etching technique,or other directional etching technique may be used. In some embodiments,a wet etching technique, an isotropic etching technique, or othertechnique may be used to remove the second portion 700.

In a fifth step 310 in FIG. 3, an etching process may be used to etchaway a third portion of the drain layer 406 and the channel layer 404.FIG. 8 is a diagrammatic sectional view of a structure formed using afifth step 310 of the method 300 of FIG. 3, in accordance with variousembodiments. In FIG. 8, the etching process of the fifth step 310 ofFIG. 3 has removed the third portion (shown at 800) down to thepassivation layer 118, so as to form the channel region 104 from thechannel layer 404 shown in FIG. 7 and the drain region 102 from thedrain layer 406 shown in FIG. 7. As with the other etchings describedabove, a mesa etching technique, an anisotropic etching technique, orother directional etching technique may be used in some embodiments. Insome embodiments, a wet etching technique, an isotropic etchingtechnique, or other technique may be used to remove the third portion800.

At a sixth step 312 of the method 300 of FIG. 3, the gate oxide layer116, the gate region 114, the source contact 120, and the drain contact122 may be formed. FIG. 9 (and also FIG. 1) is a diagrammatic sectionalview of a structure formed using a sixth step 312 of the method 300 ofFIG. 3, in accordance with various embodiments. In FIG. 9, the gateoxide layer 116 is formed that may overlie or otherwise at leastpartially covers the source region 108, the tunnel region 106, thepassivation layer 118, the channel region 104, and the drain region 102in some embodiments. Also in FIG. 9, the gate region 114 may be formedover the gate oxide layer 116, and in some embodiments, may horizontallyoverlap at least some of the tunnel region 106 and the channel region104. Standard techniques may be used in some embodiments to form thegate oxide layer 116 and the gate region 114.

At least some of the gate oxide layer 116 that overlies the sourceregion 108 and the drain region 102 may then be removed, so that thesource contact 120 can be formed over the source region 108 and thedrain contact 122 can be formed over the drain region 102, such as shownin a completed TFET 100 of FIG. 1.

FIG. 10 is flowchart of a method 1000 of operating the TFET 100 of FIG.1, in accordance with various embodiments. At 1002, such as during anOFF-state of the TFET 1000, an OFF-state leakage current flow (in acurrent flow direction between the source region 108 and the drainregion 102 through the tunnel region 106 and the channel region 104 andoutside the gate control and the gate region 114) may be reduced usingthe oxide region 110 as an insulator to remove at least some tunnelingeffect of the tunnel region 106 under the drain region 102.

At 1004, such as during an ON-state of the TFET 100, an ON-state currentflow (between the source region 108 and the drain region 102 through thechannel region 104 and the tunnel region 106) may be increased.According to various embodiments, the increased ON-state current flowmay be enabled by a decreased thickness of the channel region 104 due tothe oxide region 110 being used to reduce the OFF-state current flow.

FIG. 11 is a block diagram illustrating an example of a computing device1100 that is arranged for performing the method 1000 of FIG. 10 tooperate the TFET 100 in accordance with the present disclosure. Forexample, the computing device 1100 may include one or more componentsthat utilize/operate an embodiment of the TFET 100. In a very basicconfiguration 1102, computing device 1100 typically includes one or moreprocessors 1104 and a system memory 1106. A memory bus 1108 may be usedfor communicating between processor 1104 and system memory 1106.

Depending on the desired configuration, processor 1104 may be of anytype including but not limited to a microprocessor (μP), amicrocontroller (μC), a digital signal processor (DSP), or anycombination thereof. Processor 1104 may include one more levels ofcaching, such as a level one cache 1110 and a level two cache 1112, aprocessor core 1114, and registers 1116. An example processor core 1114may include an arithmetic logic unit (ALU), a floating point unit (FPU),a digital signal processing core (DSP Core), or any combination thereof.An example memory controller 1118 may also be used with processor 1104,or in some implementations memory controller 1118 may be an internalpart of processor 1104.

Depending on the desired configuration, system memory 1106 may be of anytype including but not limited to volatile memory (such as RAM),non-volatile memory (such as ROM, flash memory, etc.) or any combinationthereof. System memory 1106 may include an operating system 1120, one ormore applications 1122, and program data 1124. In some embodiments,application 1122 may be arranged to operate with program data 1124 onoperating system 1120. This described basic configuration 1102 isillustrated in FIG. 11 by those components within the inner dashed line.

Computing device 1100 may have additional features or functionality, andadditional interfaces to facilitate communications between basicconfiguration 1102 and any required devices and interfaces. For example,a bus/interface controller 1130 may be used to facilitate communicationsbetween basic configuration 1102 and one or more data storage devices1132 via a storage interface bus 1134. Data storage devices 1132 may beremovable storage devices 1136, non-removable storage devices 1138, or acombination thereof. Examples of removable storage and non-removablestorage devices include magnetic disk devices such as flexible diskdrives and hard-disk drives (HDD), optical disk drives such as compactdisk (CD) drives or digital versatile disk (DVD) drives, solid statedrives (SSD), and tape drives to name a few. Example computer storagemedia may include volatile and nonvolatile, removable and non-removablemedia implemented in any method or technology for storage ofinformation, such as computer readable instructions, data structures,program modules, or other data.

System memory 1106, removable storage devices 1136 and non-removablestorage devices 1138 are examples of computer storage media. Computerstorage media includes, but is not limited to, RAM, ROM, EEPROM, flashmemory or other memory technology, CD-ROM, digital versatile disks (DVD)or other optical storage, magnetic cassettes, magnetic tape, magneticdisk storage or other magnetic storage devices, or any other mediumwhich may be used to store the desired information and which may beaccessed by computing device 1100. Any such computer storage media maybe part of computing device 1100.

Computing device 1100 may also include an interface bus 1140 forfacilitating communication from various interface devices (e.g., outputdevices 1142, peripheral interfaces 1144, and communication devices1146) to basic configuration 1102 via bus/interface controller 1130.Example output devices 1142 include a graphics processing unit 1148 andan audio processing unit 1150, which may be configured to communicate tovarious external devices such as a display or speakers via one or moreA/V ports 1152. Example peripheral interfaces 1144 include a serialinterface controller 1154 or a parallel interface controller 1156, whichmay be configured to communicate with external devices such as inputdevices (e.g., keyboard, mouse, pen, voice input device, touch inputdevice, etc.) or other peripheral devices (e.g., printer, scanner, etc.)via one or more I/O ports 1158. An example communication device 1146includes a network controller 1160, which may be arranged to facilitatecommunications with one or more other computing devices 1162 over anetwork communication link via one or more communication ports 1164.

The network communication link may be one example of a communicationmedia. Communication media may typically be embodied by computerreadable instructions, data structures, program modules, or other datain a modulated data signal, such as a carrier wave or other transportmechanism, and may include any information delivery media. A “modulateddata signal” may be a signal that has one or more of its characteristicsset or changed in such a manner as to encode information in the signal.By way of example, and not limitation, communication media may includewired media such as a wired network or direct-wired connection, andwireless media such as acoustic, radio frequency (RF), microwave,infrared (IR) and other wireless media. The term computer readable mediaas used herein may include both storage media and communication media.

Computing device 1100 may be implemented as a portion of a small-formfactor portable (or mobile) electronic device such as a cell phone, apersonal data assistant (PDA), a personal media player device, awireless web-watch device, a personal headset device, an applicationspecific device, or a hybrid device that include any of the abovefunctions. Computing device 1100 may also be implemented as a personalcomputer including both laptop computer and non-laptop computerconfigurations.

Although the present disclosure has been described in terms of theabove-illustrated embodiments, it will be appreciated that a widevariety of alternate and/or equivalent implementations calculated toachieve the same purposes may be substituted for the embodiments shownand described without departing from the scope of the presentdisclosure. It is readily appreciated that embodiments in accordancewith the present disclosure may be implemented in a very wide variety ofembodiments. This description is intended to be regarded as illustrativeinstead of restrictive.

What is claimed is:
 1. A tunnel field-effect transistor (TFET),comprising: a source region; a drain region; a channel region coupled tothe drain region; a tunnel region having a portion coupled to thechannel region; and an oxide region positioned at least partially underthe drain region, the channel region, and the portion of the tunnelregion, the oxide region further being positioned laterally relative tothe source region.
 2. The TFET of claim 1, wherein the oxide region ismade from a group III-V compound material that has been oxidized.
 3. TheTFET of claim 2, wherein the group III-V compound material includesindium gallium arsenide (InGaAs).
 4. The TFET of claim 2, wherein thegroup III-V compound material that has been oxidized is substantiallysimilar to a group III-V compound material of the source region.
 5. TheTFET of claim 1, wherein the oxide region is positioned to underliesubstantially an entirety of the drain region.
 6. The TFET of claim 1,wherein the oxide region is positioned to operate as an insulator toreduce an OFF-state leakage current flow during an OFF-state of theTFET.
 7. The TFET of claim 6, wherein the oxide region enables athickness of the channel region to be approximately 1 nm-50 nm so as toincrease, during an ON-state of the TFET, an ON-state current flowbetween the source region and the drain region through the channelregion having the decreased thickness.
 8. The TFET of claim 1, furthercomprising: a gate region that overlaps with at least some of thechannel region and at least some of the tunnel region; a passivationlayer positioned between the tunnel region and the gate region; and agate oxide layer positioned between the gate region and the at leastsome of the tunnel region, or between the gate region and the at leastsome of the channel region.
 9. The TFET of claim 8, wherein: the drainregion is made from a heavily doped group III-V compound material of afirst conductivity type; the channel region is made from a lightly dopedgroup III-V compound material of the first conductivity type; thepassivation layer is made from a compound material of the firstconductivity type; the tunnel region is made from another heavily dopedgroup III-V compound material of the first conductivity type; and thesource region is made from a heavily doped group III-V compound materialof a second conductivity type different from the first conductivitytype.
 10. The TFET of claim 9, wherein the first conductivity type is ann-type material, and wherein the second conductivity type is a p-typematerial.
 11. A method to operate a tunnel field-effect transistor(TFET) having a drain region, a source region, a channel region, and atunnel region, the method comprising: during an OFF-state of the TFET,reducing an OFF-state leakage current flow, in a current flow directionbetween the source region and the drain region through the tunnel regionand the channel region, using an oxide region as an insulator to removeat least some tunneling effect of the tunnel region under the drainregion, wherein the oxide region is positioned at least partially underthe drain region, the channel region, and a portion of the tunnelregion, the oxide region further being positioned laterally relative tothe source region; and during an ON-state of the TFET, increasing anON-state current flow between the source region and the drain regionthrough the channel region and the tunnel region, the increased ON-statecurrent flow being enabled by a decreased thickness of the channelregion due to the oxide region being used to reduce the OFF-statecurrent flow.
 12. The method of claim 11, wherein the oxide region ismade from a group III-V compound material that has been oxidized. 13.The method of claim 12, wherein at least one of the drain region, thesource region, the channel region, and the tunnel region is also madefrom a group III-V compound material.
 14. A process to manufacture atunnel field-effect transistor (TFET), the process comprising: forming asource layer, a tunnel layer, a channel layer, and a drain layer over asubstrate; etching away a first portion of the drain, channel, tunnel,and source layers down to the substrate; and laterally oxidizing atleast some of the source layer, next to the etched away first portion ofthe source layer, to form an oxide region, the oxide region underlyingthe tunnel layer, the channel layer, and the drain layer and beinglaterally positioned relative to the source layer.
 15. The process ofclaim 14, further comprising: forming a passivation layer between thechannel layer and the tunnel layer; etching away a second portion of thedrain layer, the channel layer, and the tunnel layer down to the sourcelayer to form a source region from the source layer and a tunnel regionfrom the tunnel layer; and etching away a third portion of the drainlayer and the channel layer to form a tunnel region from the tunnellayer, a channel region from the channel layer, and a drain region fromthe drain layer, wherein: said etching away the first portion furtherincludes etching away a first portion of the passivation layer; saidetching away the second portion further includes etching away a secondportion of the passivation layer; and said etching away the thirdportion includes etching away the third portion down to the passivationlayer.
 16. The process of claim 15, further comprising: forming a gateoxide layer that at least partially covers the tunnel region and thechannel region; forming a gate region over the gate oxide layer and thatoverlaps at least some of the tunnel region and at least some of thechannel region; and forming a source contact on the source region and adrain contact on the drain region.
 17. The process of claim 14, whereinthe oxide region is made from a group III-V compound material that hasbeen oxidized by said laterally oxidizing.
 18. The process of claim 17,wherein at least one of the drain region, the source region, the channelregion, and the tunnel region is also made from a group III-V compoundmaterial.
 19. The process of claim 14, wherein said laterally oxidizingis performed at a time and at a temperature sufficient to form the oxideregion to underlie substantially an entirety of the drain region. 20.The process of claim 14, wherein said forming the channel layer includesforming the channel layer to have a thickness of approximately 1 nm-50nm.
 21. The process of claim 14 wherein said laterally oxidizing to formthe oxide region includes forming the oxide region to have a width thatdiffers from a width of a drain region, formed from the drain layer, byapproximately 3% to 30%.